These studies are designed to assess prospectively preferred methods of therapy and long-term sequelae of bacterial meningitis in children in whom the etiologic diagnosis has been made rapidly and whose treatment has been provided according to specific protocols supervised by specialists in pediatric infectious diseases and neurology. New insights into the pathogenesis of Hemophilus influenzae meningitis will be sought. In particular, antigenic stimuli provided by H. influenzae disease will be quantitated and correlated with antibody responses in the same children in an attempt to gain information which may be important in the ultimate development and application of effective H. influenzae vaccines for the prevention of H. influenzae meningitis in infancy and childhood. The interaction of phagocytes, phagocyte stimulators, and antibody to capsular polyribosephosphate (PRP) of H. influenzae, type b will be evaluated. An attempt will be made to determine the importance of cellular adherence in the response of children of various ages to H. influenzae infection. Sequential studies of secretion of antidiuretic hormone in children with meningitis and approaches to the modification of its secretion will be conducted. The importance of preceding or concurrent viral nasopharyngeal colonization or infection in the pathogenesis of bacterial meningitis will be evaluated. Long-term sequelae of viral meningoencephalitis also will be sought.